The present invention relates to coated seeds.
In the fields of agriculture and forestry there is no exception to the rule that labor savings constitute a major factor in cost reduction. Taking the sowing of vegetable and other seeds as an example, for the purpose of achieving machine sowing as precise as hand sowing and thereby conserving labor requirements, it has been practiced since some years ago to coat seeds with a coating mass such as red earth, clay, perlite, diatomaceous earth, calcium carbonate, talc, calcium hydroxide, aluminum hydroxide, kaolin, etc., with or without the addition of a binder such as polyvinyl alcohol, starch, carboxymethylcellulose, gelatin or the like, by means of a fluidized-bed granulator or a rotary pan (e.g. Japanese Patent Publication No. 38-3469).
When the coated seed thus prepared is sown and, hence, encounters a certain amount of water in the soil, its coating layer absorbs water to undergo cracking in a few positions and is disintegrated into pieces, thus allowing the seed to germinate. However, when the soil is over-moist after a rainfall or due to poor drainage, for instance, the coating layer containing a tacky binder melts under the influence of excessive moisture and encapsulates the seed to prevent the access of oxygen which is essential to the energy metabolism during germination and consequently precludes the normal course of germination.
In order to resolve the above-mentioned problems, there has been proposed a technique which comprises incorporating a water-repellent or water-proofing compound such as oil, fat, cellulose ester, vinyl resin, urethane resin, aluminum acetate, aluminum formate, a zirconium compound, or a higher fatty acid, inclusive of a metal salt thereof, in the coating mass composition to be used for the formation of a coating layer (e.g. Japanese. Patent Publication No. 38-3469, Japanese Kokai Patent Publication No. 54-85908, Japanese Kokai Patent Publication No. 60-129051and British Patent No. 1294161).
However, the simple coating of seeds with a coating mass composition comprising the conventional coating material in combination with such a water-repellent or water-proofing compound (hereinafter referred to collectively as a hydrophobic compound) does not insure a balanced assortment of characteristics necessary for coated seeds, such as adequate hardness, optimal mode of cracking upon absorption of water (disintegration pattern), shape retentivity after cracking into blocks upon absorption of water (the condition in which the coating layer does not stick around to the seed as a muddy mass that precludes contact of the seed with water and atmosphere). Moreover, this method hardly provides for germination characteristics comparable to those of the uncoated seeds. The use of an organic binder for imparting an appropriate degree of hardness to the coating layer is undesirable from the standpoint of production efficiency or shape retention after cracking.